Field of the Invention
The present invention relates to a fixing apparatus used in an image forming apparatus such as an electrophotographic copying machine and an electrophotographic printer.
Description of the Related Art
As fixing apparatuses installed in image forming apparatuses such as copying machines and printers using electrophotographic techniques, ones including fixing rollers which are heated from their outer circumferential surfaces are known. The fixing apparatus generally includes a fixing roller, a heating rotation member for heating the fixing roller by coming into contact with the fixing roller, and a pressing roller for forming a nip portion by coming into contact with the fixing roller. A recording material on which a toner image is formed is conveyed to and heated at the nip portion, and thus the toner image is fixed to the recording material. As the heating rotation member of the fixing apparatus, there are a member including a cylindrical film and a heater coming into contact with an inner surface of the film, a member including a heating roller equipped with a halogen heater, and the like.
In the fixing apparatus, an event referred to as an offset may occur in some cases in which a portion of a toner on a recording material is transferred to an outer circumferential surface of the fixing roller. In this specification, a toner causing an offset is referred to as an offset toner. The offset toner may be transferred to and accumulated on a surface of the heating rotation member with the rotation of the fixing roller. The accumulated toner may form a lump and soil a toner image on a recording material by irregularly returning to a surface of the fixing roller.
Thus, a fixing apparatus is described in Japanese Patent Application Laid-Open No. 2003-114583 in which a non-adhesive property of a heating member with respect to a toner on a recording material is set higher than a non-adhesive property of a fixing roller. In the fixing apparatus, adhesive force between the offset toner and the fixing roller exceeds adhesive force between the offset toner and the heating member, and thus the offset toner on the fixing roller remains on the surface of the fixing roller without adhering to the heating member. Accordingly, the offset toner on the fixing roller surface can be fixed to the recording material with the rotation of the fixing roller and discharged.
However, there is an issue that it is not enough to differentiate a non-adhesive property of an external heating member and a non-adhesive property of the fixing roller surface in some cases, and the offset toner adheres to the external heating member.